The present invention pertains generally to the amplification of steel-stringed musical instruments and more specifically to amplification of steel-stringed musical instruments using transducers sensitive to both body and string sounds.
The use of string-sensitive magnetic pickups to amplify stringed musical instruments is well known. Magnetic pickups have a distinctive sound that is valued by many players. Magnetic pickups are primarily responsive to the motion of the metal string itself within the pickup's magnetic field, therein termed “string sound”, and are only slightly responsive to mechanical vibrations of the musical instrument, herein termed “body sound”. This is a limitation when trying to reproduce all the complexities of a musical instrument, and is especially limiting on an acoustic musical instrument, since the tonal character of an acoustic instrument is largely created by the mechanical amplification and resonances of the instrument's body.
String-sensitive magnetic pickups may have several disadvantages. A string-sensitive magnetic pickup is insensitive to the tonal character of a resonant body of an acoustic musical instrument. In addition, string-sensitive magnetic pickups are also relatively insensitive to incidental sounds that contribute greatly to the realism of the amplified sound, such as finger noise and the player's deliberate taps on the body of a musical instrument.
Body-sensitive pickups may suffer from several disadvantages. For example, when an acoustic musical instrument is amplified, a feedback loop may be created that includes the amplifier, the speakers, the musical instrument's body, and the body pickup. Such a system will tend to oscillate uncontrollably at the resonant frequencies of the musical instrument's body, making the musical instrument unusable above a certain volume level. When a body-sensitive pickup is amplified enough to be heard along with other amplified instruments, such feedback is very likely and becomes a real problem. In addition, a body-sensitive pickup may only pick up certain frequencies from the part of the body to which it is attached, and thus will not have the full sound of the musical instrument. Specifically, body-sensitive pickups tend to have an excess of midrange response, a lack of response to the fundamental (lowest) frequencies of the musical instrument's string vibration, a more “distant” sound because it takes a certain amount of time for the body to respond to the strings, and a lack of immediate response (attack) when the player strikes the string. Finally, body-sensitive pickups tend to reproduce too much incidental noise, emphasizing taps and finger squeaks more than is needed for realistic reproduction.
Attempts to add body sound to magnetic pickups have been made, by mixing body-sensitive pickups such as microphones or piezoelectric transducers with the sound of the magnetic pickup. For example, U.S. Pat. No. 4,501,186 issued to Ikuma describes a mixing system that combines a magnetic pickup in a soundhole of an acoustic musical instrument with a piezoelectric transducer attached to the body of the musical instrument. This approach requires separate string-sensitive and body-sensitive transducers, electronic amplification and mixing, and extra power supplies such as batteries in the musical instrument or pickup, each of which adds cost, complexity and inconvenience. Such systems also contribute noise to the signal.
Another attempt to add body sound to string sound is described in U.S. Pat. No. 3,725,561 issued to Paul. Paul describes a magnetic pickup with a ferromagnetic mass suspended in an elastomeric material below the coil. The coil is attached to the musical instrument's body. The mass remains relatively stationary because of its inertia, and the coil moves relative to the mass. This induces a small amount of signal in the coil that is responsive to body vibration. However, this method reproduces primarily the lower frequencies of the body vibration. The amount of body-vibration signal it contributes to the total pickup sound is subtle and difficult to hear.